Comparative corrosion study of HVOF coated Wc-10Co-4Cr, NiCrBSi and NiCr industrial waste coatings on AiSi304 stainless steel

Abstract

The increasing demand for the high-velocity oxy-fuel (HVOF) thermal sprayed coated steel for boiler tube applications is the driving force behind this research work. Following the needs of the industry, the present study is aimed at understanding and comparing the corrosion resistance behavior of the WC-10Co-4Cr, NiCrBSi, and NiCrIW coating on AISI 304 stainless steel. A detailed microstructural characterization of the coatings before and after the corrosion experiment by FESEM, phase identification by XRD, and porosity determination by image analysis was performed. Corrosion behaviors of the coatings are examined by the electrochemical measurement technique after their immersion in a solution of 4 % NaCl for 1 hr, 12 hr, 36 hr, 102 hr, 200 hr, and 250 hr. Electrochemical impendence spectroscopy and Potentiodynamic polarization test results show that the porosity of the coatings and interface between unmelted particle and matrix (Formation of micro-galvanic cell) are potential sites for corrosion initiation. Electrochemical impedance spectroscopy (EIS) data indicates that the corrosion resistance of all types of coating initially decreases with increasing immersion time, but after some time corrosion resistance of the coatings again increases with increasing immersion time. This is because of the local accumulation of corrosion products in the defects hindering penetration of the electrolyte easily. Both the corrosion studies revealed that corrosion resistance of the coatings is in the following order: NiCrBSi > WC-10Co-4Cr > NiCrIW.